APIC/Fabric Discovery Process II

In this discovery process, a fabric node is considered active when the APIC and node can exchange heartbeats through the Intra-Fabric Messaging (IFM) process. The IFM process is also used by the APIC to push policy to the fabric leaf nodes.

Fabric discovery happens in three stages. The leaf node directly connected to the APIC is discovered in the first stage. The second stage of discovery brings in the spines connected to that initial seed leaf. Then the third stage processes the discovery of the other leaf nodes and APICs in the cluster.

The diagram below illustrates the discovery process for switches that are directly connected to the APIC. Coverage of specific verification for other parts of the process will be presented later in the chapter.

The steps are:

Link Layer Discovery Protocol (LLDP) Neighbor Discovery
Tunnel End Point (TEP) IP address assignment to the node
Node software upgraded if necessary
Policy Element IFM Setup


During fabric registration and initialization a port might transition to an “out-of-service” state. Once a port has transitioned to an out-of-service status, only DHCP and CDP/LLDP protocols are allowed to be transmitted. Below is a description of each out-of-service issue that may be encountered:

fabric-domain-mismatch – Adjacent node belongs to a different fabric
ctrlr-uuid-mismatch – APIC UUID mismatch (duplicate APIC ID)
wiring-mismatch – Invalid connection (Leaf to Leaf, Spine to non-leaf, Leaf fabric port to non-spine etc.)
adjaceny-not-detected – No LLDP adjacency on fabric port
Ports can go out-of-service due to wiring issues. Wiring Issues get reported through the lldpIf object information on this object can be browsed at the following object location in the MIT: /mit/sys/lldp/inst/if-[eth1/1]/summary.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s